Method for anodizing magnesium products

ABSTRACT

A method for anodizing magnesium products, the method includes the steps of: providing an electrolyte, the electrolyte including a base solution, a blackening agent, and a complexing agent; putting a substrate material as an anode in the electrolyte, and putting another material as a cathode in the electrolyte; and supplying power between the anode and the cathode until a black coating is formed on the substrate material.

CROSS-REFERENCES TO RELATED APPLICATION

Relevant subject matter is disclosed in the co-pending U.S. patent application (Attorney Docket No. US10824) filed on the same date and entitled “ELECTROLYTE FOR ANODIZING MAGNESIUM PRODUCTS”, which is assigned to the same assignee with this patent application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for anodizing magnesium products.

2. Description of Related Art

Magnesium is widely used in industry because of its low specific gravity, excellent electro magnetic interference (EMI) shielding capability, and adaptability to volume production. Typically, magnesium products require surface treatment, to protect and enhance wearability and inoxidability of their surfaces.

To address aforementioned requirement, the practice of coating magnesium materials with a thin layer is used. China Patent No. 86108405 discloses a method, and an electrolyte for anodizing magnesium products. The electrolyte includes alkali silicate (such as potassium metasilicate), alkali hydroxide (such as potassium hydroxide), and fluoride (such as potassium fluoride). A magnesium material and an auxiliary cathode are put in the electrolyte, and power is supplied between the magnesium material and the auxiliary cathode. Ceramic coating consisting of magnesia is formed on the surface of the magnesium material by spark discharge between the magnesium material and the auxiliary cathode. However, the ceramic coating on the magnesium material is white, it needs to be painted when the magnesium material is used in a dark colored product for aesthetic reasons.

What is needed, therefore, is a method for anodizing magnesium products with a black coating.

SUMMARY OF THE INVENTION

An exemplary method is provided for anodizing magnesium products. The method includes the steps of: providing an electrolyte, the electrolyte including a base solution, a blackening agent, and a complexing agent; putting a substrate material as an anode in the electrolyte, and putting another material as a cathode in the electrolyte; and supplying power between the anode and the cathode until a black coating is formed on the substrate material.

Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments, in which:

DETAILED DESCRIPTION OF THE INVENTION

A method for anodizing magnesium products in accordance with a preferred embodiment of the present invention is provided. The method includes the steps of: putting a magnesium alloy substrate material as an anode in an electrolyte, putting another metal (such as stainless steel, or other infusible inert metal) as a cathode in the electrolyte, and supplying power between the anode and the cathode until a black coating is formed on the magnesium alloy substrate material by the means of spark discharge. The electrolyte includes a base solution, a main blackening agent, an auxiliary blackening agent, a complexing agent, and an inhibitor. Temperature of the electrolyte is preferably kept between 10 to 60 degrees Celsius (° C.).

The base solution includes 2 to 25 grams of alkali per liter (g/l), 1 to 30 g/l of fluoride, 1 to 35 g/l of silicate, and water. The alkali includes at least one item selected from the group consisting of potassium hydroxide, and sodium hydroxide. The fluoride includes at least one item selected from the group consisting of potassium fluoride, sodium fluoride, ammonium fluoride, and other compounds including fluorinion. The silicate includes at least one item selected from the group consisting of potassium metasilicate, sodium silicate, potassium fluosilicate, and sodium fluosilicate.

The main blackening agent mainly includes cupric salt. The cupric salt includes at least one item selected from the group consisting of cupric hydroxide, basic copper carbonate, cupric pyrophosphate, cupric citrate, and other metal salts including cupric ions. Concentration of the cupric salt is from 0.3 to 9 g/l.

The auxiliary blackening agent includes at least one item selected from the group consisting of nickel nitrate, ammonium molybdate, ammonium metavanadate, and other oxysalts. Concentration of the auxiliary blackening agent is from 0.1 to 8 g/l.

The complexing agent includes at least one item selected from the group consisting of acid and salt of ammonia, ethylenediamine tetracetic acid (EDTA), citric acid, tartaric acid, ethylenediamine, and trolamine. Concentration of the complexing agent is from 0.5 to 20 g/l.

The inhibitor included in the electrolyte works to increase blackening, and prevent corrosion of the magnesium product. The inhibitor includes at least one item selected from the group consisting of thiourea, sodium m-nitrobenzene sulfonate, and methenamine. Each of the group consisting of thiourea, sodium m-nitrobenzene sulfonate, and methenamine includes amido, hydroxyl, nitryl, or other adsorbing radicals. Concentration of the inhibitor is from 0 to 5 g/l.

The present invention may be explained by means of the following embodiment examples:

EXAMPLE 1 Composition of the Electrolyte:

sodium hydroxide 25 g/l sodium silicate 1 g/l potassium fluoride 10 g/l cupric pyrophosphate 4 g/l nickel nitrate 0.1 g/l sodium citrate 8 g/l thiourea 1 g/l

Temperature of the electrolyte is held at 35° C.;

Color of the coating formed on the magnesium product: black; Thickness of the coating formed on the magnesium product: 10 micrometers (μm).

EXAMPLE 2 Composition of the Electrolyte:

sodium hydroxide 13 g/l sodium silicate 8 g/l potassium fluoride 13 g/l cupric pyrophosphate 1.8 g/l nickel nitrate 0.1 g/l sodium citrate 5 g/l thiourea 0.1 g/l

Temperature of the electrolyte is held at 25° C.;

Color of the coating formed on the magnesium product: black; Thickness of the coating formed on the magnesium product: 14 μm.

EXAMPLE 3 Composition of the Electrolyte:

potassium hydroxide 2 g/l sodium silicate 35 g/l potassium fluoride 1 g/l cupric pyrophosphate 6 g/l nickel nitrate 0.1 g/l disodium ethylenediamine tetraacetate 3 g/l methenamine 0.1 g/l

Temperature of the electrolyte is held at 60° C.;

Color of the coating formed on the magnesium product: reddish black; Thickness of the coating formed on the magnesium product: 14 μm.

EXAMPLE 4 Composition of the Electrolyte:

sodium hydroxide 15 g/l sodium silicate 21 g/l potassium fluoride 10 g/l cupric hydroxide 0.3 g/l ammonium molybdate 1 g/l ethylenediamine 0.5 g/l thiourea 1 g/l

Temperature of the electrolyte is held at 35° C.;

Color of the coating formed on the magnesium product: black; Thickness of the coating formed on the magnesium product: 8 μm.

EXAMPLE 5 Composition of the Electrolyte:

sodium hydroxide 3 g/l sodium silicate 4 g/l potassium fluoride 30 g/l cupric hydroxide 4.5 g/l ammonium molybdate 0.6 g/l ethylenediamine 0.5 g/l sodium citrate 8 g/l thiourea 1.5 g/l

Temperature of the electrolyte is held at 35° C.;

Color of the coating formed on the magnesium product: black; Thickness of the coating formed on the magnesium product: 12 μm.

EXAMPLE 6 Composition of the Electrolyte:

potassium hydroxide 15 g/l sodium silicate 21 g/l potassium fluoride 10 g/l cupric hydroxide 1 g/l cupric pyrophosphate 8 g/l ammonium metavanadate 4 g/l ethylenediamine 5 g/l sodium citrate 15 g/l thiourea 1 g/l

Temperature of the electrolyte is held at 35° C.;

Color of the coating formed on the magnesium product: bluish black; Thickness of the coating formed on the magnesium product: 18 μm.

EXAMPLE 7 Composition of the Electrolyte:

potassium hydroxide 15 g/l sodium silicate 3 g/l potassium fluoride 15 g/l cupric pyrophosphate 1 g/l ammonium metavanadate 8 g/l ethylenediamine 2 g/l potassium sodium tartrate 12 g/l

Temperature of the electrolyte is held at 35° C.;

Color of the coating formed on the magnesium product: black; Thickness of the coating formed on the magnesium product: 11 μm.

EXAMPLE 8 Composition of the Electrolyte:

potassium hydroxide 25 g/l sodium silicate 11 g/l potassium fluoride 10 g/l cupric hydroxide 1 g/l cupric pyrophosphate 2 g/l ammonium metavanadate 2 g/l ethylenediamine 1 g/l sodium citrate 8 g/l thiourea 1 g/l Methenamine 4 g/l

Temperature of the electrolyte is held at 10° C.;

Color of the coating formed on the magnesium product: black; Thickness of the coating formed on the magnesium product: 5 μm.

It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention. 

1. A method for anodizing magnesium products, the method comprising the steps of: providing an electrolyte, the electrolyte comprising a base solution, a blackening agent, and a complexing agent; putting a magnesium alloy substrate material as an anode in the electrolyte, and putting another metal as a cathode in the electrolyte; and supplying power between the anode and the cathode until a black coating is formed on the magnesium alloy substrate material.
 2. The method as claimed in claim 1, wherein the base solution comprises alkali, fluoride, and silicate.
 3. The method as claimed in claim 2, wherein the alkali comprises at least one item selected from the group consisting of potassium hydroxide, and sodium hydroxide, and concentration of the alkali is from 2 to 25 grams per liter (g/l).
 4. The method as claimed in claim 2, wherein the fluoride comprises at least one item selected from the group consisting of potassium fluoride, sodium fluoride, and ammonium fluoride, and concentration of the fluoride is from 1 to 30 grams per liter (g/l).
 5. The method as claimed in claim 2, wherein the silicate comprises at least one item selected from the group consisting of potassium metasilicate, sodium silicate, potassium fluosilicate, and sodium fluosilicate, concentration of the silicate is from 1 to 35 grams per liter (g/l).
 6. The method as claimed in claim 1, wherein the blackening agent comprises a main blackening agent, the main blackening agent mainly comprises cupric salt, and concentration of the cupric salt is from 0.3 to 9 grams per liter (g/l).
 7. The method as claimed in claim 6, wherein the cupric salt comprises at least one item selected from the group consisting of cupric hydroxide, basic copper carbonate, cupric pyrophosphate, and cupric citrate.
 8. The method as claimed in claim 6, wherein the blackening agent further comprises an auxiliary blackening agent, the auxiliary blackening agent is oxysalt, and concentration of the oxysalt is from 0.1 to 8 g/l.
 9. The method as claimed in claim 8, wherein the oxysalt comprises at least one item selected from the group consisting of nickel nitrate, ammonium molybdate, and ammonium metavanadate.
 10. The method as claimed in claim 1, wherein the complexing agent comprises at least one item selected from the group consisting of acid and salt of ammonia, ethylenediamine tetracetic acid (EDTA), citric acid, tartaric acid, ethylenediamine, and trolamine, concentration of the complexing agent is from 0.5 to 20 grams per liter (g/l).
 11. The method as claimed in claim 1, wherein the electrolyte further comprises an inhibitor for increase of blackening and preventing corrosion of the substrate material, the inhibitor comprises at least one item selected from the group consisting of thiourea, sodium m-nitrobenzene sulfonate, and methenamine, each of the thiourea, sodium m-nitrobenzene sulfonate, and methenamine including amido, hydroxyl, or nitryl absorbing radicals, concentration of the inhibitor is from 0 to 5 grams per liter (g/l).
 12. The method as claimed in claim 1, wherein temperature of the electrolyte is kept between 10 to 60 degrees Celsius (° C.).
 13. The method as claimed in claim 1, wherein thickness of the black coating is from 5 to 18 micrometers (μm).
 14. A method for anodizing magnesium products, the method comprising the steps of: providing an electrolyte, the electrolyte comprising alkali, fluoride, silicate, cupric salt, oxysalt, and complexing agent; putting a magnesium alloy substrate material as an anode in the electrolyte, and putting another metal as a cathode in the electrolyte; and supplying power between the anode and the cathode until a black coating is formed on the magnesium alloy substrate material.
 15. The method as claimed in claim 14, wherein concentration of the alkali ranges from 2 to 25 grams per liter (g/l), the fluoride from 1 to 30 g/l, the silicate from 1 to 35 g/l, the cupric salt from 0.3 to 9 g/l, the oxysalt from 0.1 to 8 g/l, and the complexing agent from 0.5 to 20 g/l.
 16. The method as claimed in claim 14, wherein the complexing agent comprises at least one item selected from the group consisting of acid and salt of ammonia, ethylenediamine tetracetic acid (EDTA), citric acid, tartaric acid, ethylenediamine, and trolamine.
 17. An electronic device, wherein the electronic device comprises a substrate made of magnesium alloy and a black coating formed on a surface of the substrate by the method of claim
 1. 18. The electronic product as claimed in claim 17, wherein the coating has a thickness in a range of 5 to 18 micrometers (μm). 